Radio signaling system



Sept 29, 1931.

DE LOSS K. MARTIN -RADIO SIGNALING SYSTEM Filed Sept. 25, 1925 BY W ATTORNEY Patented Sept. 29, 1931 DE Loss K. MARTIN, orwns'r ORANGE, NRWJRRSEY, AssGnQRmo AMERICAN PHONE AND TELReRArH comprimir, A'.c oR'oRA'rIoNy` or NEW YORK i SIGNAifINGSYT-E l l E AppinfamiaI medsptenber 25,1925. serial Ne. 58,663.

This invention relates to radio` signaling l systems, and particularly to a system of that typeintended for broadcasting purposes. itsy is well known, a pluralityfvof radio broadcasting stations are frequentlyy conneoted' by wire lines vwith what may be termed a program center,that is to say, astation where the program is put upon" the wire .circuit for transmission to each of the broadcasting stations; In the `radio broadcasting art it is 'not uncommon to connect together a plurality of broadcasting-stations which are widely separated geographically. It has been found that-the transmission of an audio frequencyf band over a long transmission line produces distortion of the band, such distortion arising fromthe characteristics of the line `and the transformers in -the 4repeating apparatus. It has been found that by raising the band to a higher position in the frequency spectrum before applying it to the wire line, it,Y is `possible to transmit vthe :band with greaterruniformity, that ist'osay, less distortion than whereaudio frequency transmis-i sionis employed. f

One of the objects of ithisinveiition is to reduce the magnitude'offthe distortion resulting from the transmission aof the *frequency bands over the wire-:network "of a multi-station Aradiobroadcasting system by raising the frequenciesfof the Vtransmitted Another object of this inventionresides in modulating the radio carrier frequency `at the broadcasting'stations directl by the intermediate frequencyv band received thereat from the-wire line. This'method eliminates distortion which'is present in those systemsl in which Lan incoming modulated 'carrierfrrequencyis demodulated tov produce the audio frequency signal .which is then 'employed to modulate the radio` frequency carrier.. In

such systems the trouble` arises --from kfthe f transmission characteristics of the audio fre'-v quen'cy circuits at the broadcasting stations which `will always, toa certain extent, distort the audio frequency bandos y l Other objects of this invention lwill`-also ybe apparent from the following description when ready .in connection with the-attached drawings, vof which Figure l shows sche-l maticallya form of'embodiment ofv the inventionto effect transmission over a wire line I Ato `a plurality of broadcastingantennae of a I carrierl frequency andalso one of the side bands of the carrier, the frequencies employed throughout the wire system being of course diEerent fromxthis transmitted' from' the antennae; andFig. Zrepresents a similarari rangement to eliect single side-band transmission over'the` lines and also from the `antennae, the bandvtransmitted over vthe line being, however, of different frequencyfrom that sent vfrom thev antennae. l

nected with three broadcasting stations designated A, B and C. It will ofcourse be understood that the invention may be embodied in a system employing any'numberfof stations. .i T he program center comprises whates termed an audio frequency pick-up,'designat ed l,r which is connected with the modulator 2, having connectedtherewith Ia sourceof oscillations 3, ofthe frequency f1.1 While the modulator and the oscillator may be of any type,a desirable formwould of course be the `vacuumtube type. The output of the modu lator .2 is connected lwith the wirev line e through the band filter 5. This filter, which is of the type shown in the patent to Camp- `bell,1,227,113, is designed 4to transmit `they carrier f1 and one ofthe side bands resulting fromlmodulation ofthecarrier frequency f1 by the audio-frequency-s, the band being represented by f1 fls.- lThe frequency f1 of the ycarrieris within the range suitable for transmission over afwire circuit, that is to say,be tween l5' and A30 kilocycles.v The wireiline 4 extends to thev broadcasting stationl A. land has therein a repeater'G-to compensate forthe attenuation of this circuit. Another wire line 7 is'connected with the Vline 4 and also'with thelinesSl and '9 to connect the stations Band YC with the program center. Repeaters 10 and yll are/included in the wire' line 7. It will of course be ,understood that the numberl of repeaters employed will depend upon theftrans- -missionlevel thatit is desiredtomaintain over'f'the system. The broadcasting station A, whichislsimilartoBL and C, comprises a ibo radio broadcasting stations, v. a .program center, and a plurality of circults connecting the said center with each of said broadcasting stations, the method which consists in modulating by an audio frequency a carrier current of intermediate frequency suitable for transmission over a wire line, Vtransmitdiate frequency carrier and the side bandV transmitted therewith over the said wire line.

2. In a system comprisinga plurality of radio broadcasting stations, a program center, and a plurality of circuits connecting the said center with each of said broadcasting stations, the method which consists in modulating by audio frequencies Va carrier current of intermediate frequency suitablefor transmission over a wire line,`selecting the carrier A frequency and one of the side bands and transmitting to each broadcasting station the said carrier and the selected side band, modulating at each broadcasting station, a radio frequency current by a band of frequency comprising the said intermediate frequency carrier and its side band, selecting and radiating one of the side bands produced by the modulation of the said radio frequency carrier by they said band of frequencies consisting of the said intermediate frequency carrier and side band transmitted therewith over the said wire line.

3. In a system comprising a plurality of radio broadcasting stations, a program center, and a plurality of circuits connecting the said center with each of saidbroadcasting stations, the method which consistsin modulating by audio frequencies a carrier current of intermediate frequency suitable for transmission over a wire line, selecting the said carrier and one side band,`transmitting to each broadcasting station the selected carrier and side band frequencies and amplifying such frequencies during thesaid transmission, modulating at eachv broadcastingstation a radio frequency carrier by a band of frequencies comprising thesaid-intermediate frequency carrier and its side band, selecting one of the side bands'produced by the modulation of the said radio frequency-carrier by ter, and a plurality of circuits connecting the said center with each of said broadcasting stations, the method which consists in modulating by audio' frequencies a carrier current of intermediate frequency suitable for transmission over a Wire line, selecting the said carrier and one side band, ltransmitting to each broadcastin station the selected carrier and side band requencies and amplifying suchA frequencies during the ysaid transmission, modulating-at each 'broadcasting station a radio frequency carrier by a band of frequencies comprising the said intermediate frequency carrier and its side band, selecting one of the side band combinations resulting from the last Vmodulating stepthe said combination comprising a broadcast carrier resulting from beating the radio frequency carrier by the intermediate frequency carrier, andv that side band resultingfrom modulating the radio frequency carrier by the intermediate frequency side band which, when beaten with the said selected broadcast car- "rier, will produce the audio frequency, and

amplifying and radiating the selected frequencles.

5. vThemethod ofefecting radio broadcast transmission of a single side band, together with its carrier to permit of ready detection of the program by broadcast receivers, which consists in modulating by the laudio frequencies of the program a carrie;

Whose frequency is intermediate between the audio'frequencies and the frequency of broadcast radiation, eliminating one of the side bands and transmitting the carrier with the remainingside band, modulating a radio frequency carrier by a band of frequencies comprising the single lside band and the first mentioned carrier, selecting and radiating one of the resulting side band combinations, comprising a carrier and a single side band, and suppressing the other components coniprising the radio frequency carrier and the Vopposite side band combination.

In testimony whereof, I have signed my` name to this specication this 23rdday of September 1925.

DE LOSS K. MARTIN.

the said band consisting kof the said intermediate frequency carrier and the side band transmitted therewith over the `said wire" i' line, and radiating the side band as thus selected.

4. In a system comprising a plurality of radio broadcasting stations, a program cen- 

